This invention relates generally to a semiconductor device and to a process for manufacturing a semiconductor device, and more specifically to an improved process for fabricating a semiconductor device using a contact plug technology and to a device incorporating the contact plug.
As the geometries utilized in the fabrication of semiconductor devices are reduced to smaller and smaller dimensions, it becomes difficult to provide a reliable contact to impurity doped electrically active regions or to other electrically conductive elements. One technique that is used to provide a contact to an underlying electrically conductive element is the contact plug technology. Electrically conductive elements are often buried beneath or within one or more dielectric layers. In the contact plug technology a hole or opening is formed through the dielectric material to expose a portion of the underlying electrically conductive element. A plug of electrically conductive material such as a metal, often tungsten metal, is formed in the opening through the dielectric material and electrically contacts the electrically conductive element. The conductive plug extends to the surface of the dielectric material where it is contacted by a patterned interconnect metal layer. Electrical contact is thus established between the electrically conductive element and the patterned interconnect metal layer.
In accordance with prior art conductive plug technologies, the plug is usually formed by chemical vapor depositing the conductive plug material in the opening formed through the dielectric material. If the plug material is tungsten, the plug is formed by the chemical vapor deposition (CVD) of tungsten, usually by reducing tungsten hexafluoride (WF6). Both WF6 and fluorine, the by-product of the reduction reaction, are highly reactive with many of the commonly used dielectric materials. As a result, the conventional plug technology requires the use of a barrier layer to protect the exposed dielectric material from unwanted reaction with the WF6 and fluorine during the CVD process. The most commonly used barrier material is a layer of titanium nitride (TiN). Although the TiN forms a satisfactory barrier layer when the contact opening through the dielectric material is of the order of 0.4 microns or greater, it is unsatisfactory when the contact opening shrinks to smaller dimensions, such as a diameter of about 0.1-0.2 microns.
TiN is unsatisfactory as a barrier material for very small contact openings for at least two reasons. First, the TiN is usually deposited to a thickness of about 10-20 nanometers (nm). Although this thickness of TiN is relatively insignificant for a large diameter contact opening (i.e., about 0.4 microns or larger), a layer of such thickness fills a considerable portion of the smaller size contact opening (i.e., a contact opening having a diameter of about 0.1-0.2 microns). Although TiN is electrically conductive, it is less so than tungsten. Because the resistance of the contact plug is inversely proportional to the cross sectional area of the contact, decreasing the diameter of the more conductive material increases the resistance through the plug. Additionally, TiN barrier layers, especially in small size contact openings, cause a problem with high contact resistance to the underlying electrically conductive element.
It should be noted that the barrier layer, in addition to functioning to protect the underlying dielectric material from unwanted reaction with the WF6 and fluorine, also functions to provide an adhesion promoter for the chemical vapor deposited tungsten layer and as a nucleating site for the uniform deposition of the deposited tungsten layer. In the absence of a nucleating material formed uniformly over the surface, the chemical vapor deposition of tungsten onto a dielectric material is difficult and produces a nonuniform and often noncontinuous tungsten layer. In addition, in the absence of an adhesion promoting layer, tungsten does not adhere well to most dielectric materials. Hence in the absence of a barrier layer/adhesion promoter, the chemical vapor deposited layer of tungsten may cause reliability problems by peeling or separating from the underlying dielectric material.
In view of the problems enumerated above with respect to the existing tungsten contact plug technologies, a need exists for a semiconductor manufacturing process that includes an improved contact plug technology that will provide a low total resistance contact to the electrically conductive element to be contacted, that will provide good adhesion of the contact plug to the adjacent dielectric materials, and that will provide a nucleating site for the deposition of a contact plug material to provide uniform and reliable contact plug deposition conditions, especially for small geometry contact openings. In addition, a need exists for an improved semiconductor device, especially a small geometry semiconductor device employing improved, low resistance contact plugs to contact electrically conductive elements.
In accordance with one embodiment of the invention, especially in view of the foregoing expressed needs, a process for manufacturing a semiconductor device is provided that includes an improved contact plug technology in which an ionized metal plasma technique is used to provide a barrier layer. The ionized metal plasma technique not only provides an acceptable barrier layer having low contact resistance, the new technique also provides a nucleating layer for the uniform deposition of the contact plug material. The barrier layer formed in this manner is also adherent to the commonly used dielectric materials. In accordance with a further embodiment of the invention, an improved semiconductor device is provided that is fabricated using the improved contact plug technology.